Sliding Contact Bearing
Thick Film Lubrication
In this, two surface of bearing in relative motion are completely separated by a film of fluid. Thus surface friction has no role, it has two types:
Hydrodynamic Bearing
In hydrodynamic bearing, load-supporting fluid is created by shape and relative motion of sliding surfaces. It is not necessary to supply the lubricant under pressure. The only requirement is sufficient and continuous supply. Its main application is in engine centrifugal pump.
Remember:
- Bearing which operate without lubricant is called zero film bearing.
- Journal Bearing: It is a sliding contact bearing working on hydro-dynamic lubrication, support the load in
radial direction. It has two types:
Hydro-Static bearing
In this system, load supporting fluid film separating two surfaces is created by external source like pump supplying sufficient fluid under pressure. Thus, it is also called externally pressurized bearing, it is used in centrifuges ball mills and vertical turbo generator.
Advantages:
- High load carrying capacity
- Starting friction is absent
- There is no rubbing action
Thin Film Lubrication
Lubricant film is relatively thin and there is partial to metal contact. In this lubrication, under excessive load, less oil supply, low speed, misalignment, boundary lubrication will occur. Performance of bearing under boundary lubrication will depend upon.
- Chemical composition of lubricating oil.
- Surface roughness.
Remember:
Under excessive load and low speed, hydro-dynamic bearing also operates under boundary lubrication.
Measurement of Viscosity
Saybolt Universal Second (SUS), Zk = 0.22t – 180/t
Here, Zk = Kinematic viscosity, t = Viscosity in SUS
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